I called it (weak yay) (Spoiler Episode 10) · 12:08am May 8th, 2017
Below is the short description of S7E10 from Screener.
"Starlight Glimmer is sent to solve a friendship problem between Princess Celestia and Princess Luna; when it's clear that the problem is that the royal sisters don't appreciate one another, Starlight impulsively switches their cutie marks!"
So Starlight does have the capability to switch cutie marks!